The invention generally relates to a modular retrievable packer.
A packer is a device that is used in an oilfield well to form a seal for purposes of controlling production, injection or treatment. In this manner, the packer is lowered downhole into the well in an unset state. However, once in the appropriate position downhole, the packer is controlled from the surface of the well to set the packer. As an example, for a mechanically-set packer, a tubular string that extends from the surface to the packer may be moved pursuant to a predefined pattern to set the packer. For a hydraulically-set packer, fluid inside the tubular string may be pressurized from the surface, creating a tubing pressure differential to set the packer.
In its set state, the packer anchors itself to the casing wall of the well and forms a seal in the annular region between the packer and the interior surface of the casing wall. This seal subdivides the annular region to form an upper annular region above the packer that is sealed off from a lower annular region below the packer. The packer also forms a seal for conduits that are inserted through the packer between the upper and lower annular regions. As examples, one of these conduits may communicate production fluid from a production zone that is located below the packer, one of the conduits may communicate control fluid through the packer, one of the conduits may house electrical wiring for a submersible pump, allow production or injection through two different reservoir zones, etc.
As a more specific example, FIG. 1 depicts a well that includes a packer 20. As shown, the packer 20 may be connected to a tubular string 16 that extends downhole into the well. The packer 20 forms an annulus seal with the interior surface of a wall of a casing string 12 that circumscribes the packer 20. The packer 20 typically includes at least one seal assembly 24 to form the annulus seal and at least one set of slips 22 to anchor the packer 20 to the casing string 12. In this manner, when run into the well, the seal assembly 24 and the slips 22 are radially retracted to allow passage of the packer 20 through the central passageway of the casing string 12. However, when the packer 20 is in the appropriate downhole position, the packer 20 is set to place the packer 20 in a state in which the seal assembly 24 and slips 22 are radially expanded. When radially expanded, the slips 22 grip the interior surface of the wall of the casing string 12 to physically anchor the packer 20 in position inside the well. The radial expansion of the seal assembly 24, in turn, seals off the annular space between the string 16 and the casing string 12 to form a sealed annular region above the seal assembly 24 and a sealed annular region below the seal assembly 24.
The packer 20 may be hydraulically actuated for purposes of controlling the packer 20 from the surface of the well to set the packer 20. This means that pressure may be communicated through fluid inside the string 16 to the packer 20. In response to this pressure reaching a predefined threshold level, pistons (not shown in FIG. 1) move to radially expand the slips 22 and apply compressive forces on the seal assembly 24 to radially expand the assembly 24. A retention mechanism of the packer 20 serves to hold the packer 20 in the set state when the pressure that is used to set the packer 20 is released.
One or more mandrels 21, or tubular elements, may extend through the packer 20 for purposes of providing communicating paths through the packer 20. Depending on the particular application of the packer 20, a particular mandrel 21 may contain one or more communication paths, such as paths to communicate production fluid, electrical lines, or control fluid through the packer 20. For example, in a particular application, a single mandrel 21 may extend through the packer 20 for purposes of communicating production fluid from a tubular string 23 located below the packer 20 to the string 16 located above the packer 20. However, in other applications, more than one mandrel 21 may be extended through the packer 20. Thus, one mandrel 21 maybe used for purposes of communicating electrical or hydraulic lines, for example, and another mandrel 21 may be used for purposes of communicating production fluid through the packer 20.
The packer 20 may be retrievable, and thus may include a release mechanism that when engaged, releases the retention mechanism of the packer 20 to radially retract the slips 22 and seal assembly 24 to permit retrieval of the packer 20 to the surface of the well.
The packer 20 establishes two general seals: an interior seal between the interior of the packer 20 and the exterior of the one or more mandrels 21 that are extended through the packer 20; and an exterior seal between the exterior of the packer 20 and the interior surface of the wall of the casing string 12. Because the mandrel configuration may change depending on the particular application of the packer, a given packer design may need to be modified to accommodate the particular application. Thus, for example, the packer 20 may have a first design for an application in which a single mandrel extends through the packer 20. However, the design of the packer 20 must be redesigned for an application in which two mandrels are extended through the packer 20. In this manner, the exterior profiles and structure that are presented by two mandrels are significantly different from the exterior profiles and structures that are associated with one mandrel, thereby requiring a substantial redesign of the packer's interior sealing rings and structure that establishes the packer's interior seal. Furthermore, the design of the packer 20 may need to be redesigned to accommodate different size mandrels or additional mandrels that are inserted through the packer 20.
Thus, there is a continuing need for an arrangement that addresses one or more of the problems that are set forth above.